1. Field of the Invention
The present invention relates to improvements in rolls for continuous casting.
2. Description of the Prior Art
Continuous casting rolls comprise a roll body and a sleeve covering the roll body. The roll body has a shaft portion at each end of its trunk portion. In accordance with the method of cooling with water and the internal construction, these rolls are classified into the sleeve type, roll end type, arbor sleeve type, etc. as shown in FIGS. 7 to 9. The rolls of any of these types, however, involve the following problems in respect of durability, etc.
The roll of the sleeve type shown in FIG. 7 comprises a roll body 1 and a sleeve 2 covering the trunk portion 1a of the roll body and fixed at one end to the roll body 1 by a weld 3. A seal ring 5 for preventing leakage of water is fastened to the other end 4 of the sleeve by screws 6. A helical cooling water channel 7 formed in the peripheral surface of the trunk portion 1a communicates, through passages 8, 8a, with cooling water bores 9, 9a extending through the opposite ends of the roll body 1 coaxially therewith. Cooling water is supplied through the bore 9, passed through the passage 8, helical channel 7 and passage 8a and discharged from the bore 9a.
With this roll, the sleeve 2 is cooled directly with the water flowing through the helical channel 7 and therefore has relatively high resistance to the heat to which it is subjected during continuous casting. However, when the sleeve 2 is fitted to the trunk portion 1a of the roll body 1 tightly, the projections defining the helical channel 7 join with the sleeve 2 firmly to hinder axial free thermal expansion or deformation of the sleeve 2. Thus the sleeve is prevented from free thermal expansion when coming into contact with hot slabs. As a result, the sleeve undergoes plastic deformation and becomes susceptible to cracking. It is therefore impossible to fit the sleeve 2 to the trunk portion 1a tightly. On the other hand, if the sleeve 2 is fitted to the trunk portion 1a loosely, the sleeve separates from the projections on the roll trunk portion 1a when expanding during continuous casting, with the result that the load is supported by the sleeve 2 only. The sleeve 2 will then fracture relatively early, permitting the cooling water to jet out.
The roll end type shown in FIG. 8 is similar to the sleeve type in construction. The trunk portion 1a of its roll body 1 comprises a hollow pipe 11 and end plates 12, 12a at the opposite ends of the pipe 11. The end plate 12a is fixed to the large-diameter end of a shaft portion 1b. The opposite ends of a sleeve 2 are secured to the roll body 1 by welds 3, 3.
Accordingly the roll has the same drawback as the sleeve type roll; the free thermal expansion of the sleeve 2 is extremely inhibited. Additionally the trunk portion of the roll body involves problems in respect of strength and is liable to fracture early.
FIG. 9 shows an arbor sleeve type roll which comprises a roll body 1 and a sleeve 2 covering the trunk portion 1a of the body and fixed at its one end to the roll body 1 with a weld 3, so that the sleeve 2 can be tightly fitted around the trunk portion 1a by a shrink fit. However, since a cooling water channel 13 extends through the roll body 1 coaxially therewith, it is impossible to cool the sleeve 2 sufficiently only with the cooling water flowing through the channel 13. When external cooling water is not used, the longitudinally middle portion of the sleeve 2 is heated to a very high temperature and becomes softened and worn markedly. Although the sleeve tends to stretch toward its free end 4 owing to thermal expansion at high temperatures, the sleeve which is tightly fitted to the roll body as stated above is restrained and is unable to stretch fully. Consequently the sleeve bulges or cracks at the middle portion, rendering the roll unserviceable in a short period of time.
The product prepared by a continuous casting process is thereafter fed to a rolling process, in which it is reheated to a specific temperature and then rolled. If it is possible to minimize the drop of the temperature in the continuous casting process and to feed the casting to the rolling process as maintained at a high temperature, the combination of the casting process and the rolling process thus connected thereto directly will achieve great savings in energy. To realize this, there is the need to reduce the amount of water used for external cooling in the continuous casting process, but the casting roll will then be subjected to a greater thermal influence. The conventional rolls described above are in no way usable for fulfilling the above object because the foregoing drawbacks become more pronounced under such conditions.